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Installation of the Cyclotron Based Clinical Neutron Therapy System in Seattle

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Installation of the Cyclotron Based Clinical Neutron Therapy System in Seattle Proceedings of the Tenth International Conference on Cyclotrons and their Applications, East Lansing, Michigan, USA INSTALLATION OF THE CYCLOTRON BASED CLINICAL NEUTRON THERAPY SYSTEM IN SEATTLE R. Risler, J. Eenmaa, J. Jacky, I. Kalet, and P. Wootton Medical Radiation Physics RC-08, University of Washington, Seattle ~ 98195, USA S. Lindbaeck Instrument AB Scanditronix, Uppsala, Sweden Sumnary radiation areas is via sliding shielding doors rather than a maze, mai nl y to save space. For the same reason A cyclotron facility has been built for cancer a single door is used to alternately close one or the treatment with fast neutrons. 50.5 MeV protons from a other therapy room. All power supplies and the control conventional, positive ion cyclotron are used to b0m­ computer are located on the second floor, above the bard a semi-thick Beryllium target located 150 am from maintenance area. The cooler room contains a heat the treatment site. Two treatment rooms are available, exchanger and other refrigeration equipment. Not shown one with a fixed horizontal beam and one with an iso­ in the diagram is the cooling tower located in another centric gantry capable of 360 degree rotation. In part of the building. Also not shown is the hot lab addition 33 51 MeV protons and 16.5 - 25.5 MeV now under construction an an area adjacent to the deuterons are generated for isotope production inside cyclotron vault. It will be used to process radio­ the cyclotron vault. The control computer is also used isotopes produced at a target station in the vault. to record and verify treatment parameters for indi­ vidual patients and to set up and monitor the actual radiation treatment. Special design requirements had to be fulfilled to allow the installation within a hospital environment. Introduction During the past decade fast neutrons have been demonstrated to be the most promising form of immedi­ ately available hospital based particle therapy beams. So far most work has been done on accelerators which were originally designed for physics research and which subsequently were adapted for use in cancer therapy. Encouraging results have led to the development of MAINTENANCE hospital based accelerator systems optimized for AREA therapy purposes. The US National cancer Institute has awarded contracts to three universities to build and operate neutron therapy facilities. One of these is located at the University Hospital in Seattle. ==o~----,!-d=~=~ =--,; =, ="U===u===;r=ii=====-:::::===:II 10..... FIRST FLOOR General Facility Lay-Out The new facility is located immediately adjacent to the existing Radiation Oncology Department which already operates four linear electron accelerators for X-ray and electron beam treatment. The department is located on the first floor of the University Hospital, ground level being at the third floor. The cyclotron facility is housed in a new underground structure in front of the hospital and can be entered through the cancer Center in the old building. Therefore up to the central waiting area the patient flow is identical for people being treated with conventional radiation and for neuron therapy patients. Fig. 1 shows the overall lay-out of the neutron therapy facility. The cyclotron vault is accessible through the maintenance area which will contain a small workshop for minor in-house repairs. Access to the two treatment rooms is through the control area with sepa­ Fig. 1 General Lay-Out of the Facility rate control consoles for the cyclotron/ beamline equipment and for therapy control. All access to the 428 CH1996-3/84/0000-0428 $1.00 ○c 1984 IEEE Proceedings of the Tenth International Conference on Cyclotrons and their Applications, East Lansing, Michigan, USA Building Accelerator Equipment The building to house the cyclotron and therapy The cyclotron is a commercial MC50 unit built by system had to accommodate the equipment and at the same Scanditronix. It can produce 33 to 51 MeV protons and time meet tight space and budget requirements. Care 16.5 to 25.5 MeV deuterons at 70 pA external current. had to be taken to integrate it architecturally with After the initial trial stage it has been decided to the demands of a patient care facility. The somewhat use a 50.5 MeV proton beam for standard therapy opera­ peculiar shape of the building reflects these restric­ tion and the Beryllium targets have been designed tions. Washington state laws for hospital installa­ accordingly. The variable energy capability and the tions required that all wiring over 30 Volt be run in deuteron option will be used for future experimental separate conduits. Cable trays could only be used for work and for isotope production. Scanditronix also low voltage signals. This required a very careful delivered the beamline equipment using Danfysik quadru­ coordination between equipment manufacturer and build­ pole triplets, bending magnets and wire-loop beam ing design team. profile monitors. Beamline height is 1200 mm through­ out the facility. All conduits and air ducts penetrating the shield­ ing walls have multiple bends to reduce radiation leakage. Special attention was given to keep neutron Neutron Therapy Equipment activation of the walls and other building parts low to reduce radiation exposure of the radiation technolo­ One of the treatment rooms is equipped with a fixed gists. Limestone aggregate was used in all shielding horizontal beam, the other with an isocentric gantry concrete and the amount of metal in walls bombarded by with 360 degree rotational capability. Both units were the primary neutron beam was kept to a minimum by using built by ELVEN Precision, England, a subcontractor of wood furring strips. These wall areas are also covered Scanditronix. The treatment heads are identical on with borated 4 em panels to reduce backscattered neu­ both units. They contain the semi-thick Beryllium tron flux from the wall. Generally the wall thickness target in which the protons lose 50% of the initial is 240 am, with 270 em in locations exposed to the energy. The remaining energy is deposited in graphite. primary neutron beam. The same applies for the ceil­ Also contained in the head are the beam flattening ing. Some walls of the cyclotron vault and the isocen­ filters, the dual dosimetry system, a wedge filter tric treatment room could be kept thinner as there is system to produce asymmetric dose distributions, the earth fill on the outside. beam defining lamp and an x-ray tube to simulate the neutron field with diagnostic x-rays for patient set­ All radiation areas are air conditioned with nega­ up. The head carries the neutron collimator which can tive pressure. No air is recirculated and the exhaust be rotated around the beam axis. In the fixed beam duct is with one exception routed outside occupied room the collimation is done with interchangeable areas to join the main building exhaust shaft. inserts, a system which is simple but awkward to handle. The isocentric unit is equipped with a vari­ The cyclotron, beamline equipment and some power able vane collimator built by Scanditronix. A total of supplies are cooled with a closed loop deionized water 40 individually powered steel leaves allow for a large system. The therapy targets have their own closed loop variety of field sizes and shapes. systems to confine higher contamination levels. In the cooler room the heat is transferred to a water/glycol In order to make the 360 degree rotation of the loop which in turn is cooled by a dedicated cooling gantry possible, a 3 m-deep pit is necessary to take up tower. A small chiller unit ensures that the cooling the head in its down position. This pit is covered by water for the oil diffusion pumps is below 20 degree C a moving floor. A system of sliding slats tracks the under all conditions. head automatically as it rotates around, leaving only small gaps. Equipment Access and Installation It is possible to rotate the gantry while the beam is running for so called arc-therapy. An automatic All large equipment components were lowered through feedback system takes beam current signals from four an access shaft near the maintenance area and then quadrants at the target location and controls an XY transferred to the final locations. The access shaft steering magnet in the gantry arm to correct for small was afterwards converted into a stairwell. If neces­ mechanical deflections during rotation and keep the sary the top can be lifted off again and the stair beam centered on target. removed for future accessibility. This solution avoids potential building leakage problems in critical areas like an access plug in the vault ceiling might have Control System created. All personnel safety interlocks are hard-wired Delivery of the treatment room equipment had to be (doors, beam plugs etc). Equipment protection inter­ tightly coordinated with construction progress, since locks are hard-wired or handled by a Gould-Modicon 484 finish work in the hallway and control area could only controller. All other functions are performed by a PDP be started after equipment move-in. The headers above 11/23 computer which interfaces with the equipment via the treatment room shielding door consist of removable the Scanditronix I/O system. The control computer concrete blocks which were installed only after the performs the following tasks: power-up/ power-down gantry main frame was passed through. sequencing, setting and monitoring of magnet currents and other parameters, display of sub-system status, Ten-ton crane rails are available in the treatment record and verify functions for patient set-up and room ceiling and all heavy lifting during installation treatment, therapy system test programs. All patient could be done using a motorized hoist. The cyclotroll treatment prescriptions are prepared on the Radiation vault bridge crane has only a 2 ton capacity and addi­ Oncology VAX 11/780 system and transferred to the tional rigging equipment was necessary to assemble the PDP 11/23 using DECNET.
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